Method for manufacturing gas sensor

ABSTRACT

Among first and second swaged sections, the second swaged section begins to be swaged prior to the first swaged section. Hence, a strong force can be prevented from acting on a rubber plug in a free state at a time and the first swaged section can begin to be swaged in such a state that a portion of the rubber plug that corresponds to the second swaged section is aligned as compared to the case where the first and second swaged sections begin to be simultaneously swaged. This prevents the position of the rubber plug from being significantly varied during swaging and also prevents the rubber plug from protruding from an outer tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2013-071829 filed in Japan on Mar. 29, 2013, the contents of which arehereby incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a method for manufacturing a gassensor.

2. Description of the Related Art

Hitherto, there have been known gas sensors for detecting theconcentration of a predetermined substance, such as NO_(R), in measuredgas such as an automobile exhaust gas. For example, Japanese UnexaminedPatent Application Publication No. 09-196885 describes a gas sensorincluding a sensor element which is placed in a tubular body made ofmetal and which detects the concentration of gas at the tip of thetubular body, a connector in contact with an electrode placed on theback end side of the sensor element, an elastic body (grommet) attachedto a back open end of the tubular body, and a lead which is connected tothe connector and which extends outward from an open end of the tubularbody through a through-hole of the elastic body.

Japanese Unexamined Patent Application Publication No. 09-196885proposes a method for manufacturing the gas sensor. In the method, theelastic body is fixed to the tubular body by multi-stage (two-stage)swaging in such a way that two sites spaced at a predetermined distancein an axial direction of the tubular body are swaged.

SUMMARY

In the case of fixing the elastic body by swaging as described above, ifswaging excessively increases the axial elongation or misalignment ofthe elastic body, then sealing properties cannot be sufficiently ensuredor a connection between the connector and the lead is misaligned; hence,electrical connectivity may possibly be adversely affected.

It is a main object of a method for manufacturing a gas sensor accordingto the present invention to ensure better sealing properties andelectrical connectivity in the case of sealing an open end of a tubularbody enclosing a sensor element by swaging an elastic body.

In order to achieve the above main object, the method for manufacturingthe gas sensor according to the present invention has taken means below.

The present invention provides a method for manufacturing a gas sensorincluding a sensor element capable of detecting the concentration ofmeasured gas; a connector electrically connected to the sensor element;a tubular body in which the sensor element and the connector are placedand which has an open end; leads which are connected to the connectorand which extend outward from the open end of the tubular body; and anelastic body which is placed in the tubular body so as to seal the openend, in which connections between the connector and the leads areplaced, and through which the leads extend, the method comprising:radially swaging the tubular body and the elastic body at a plurality ofswaged sections including a swaged section located on the connectionside and a swaged section located closer to the open end than the swagedsection located on the connection side, wherein in the swaging, amongthe plurality of swaged sections, a swaged section other than the swagedsection located on the connection side begins to be primarily swaged.

The method for manufacturing the gas sensor according to the presentinvention includes radially swaging the tubular body, which has the openend, and the elastic body, in which connections between the connectorand the leads are placed and through which the leads extend, at theswaged sections, which include the swaged section located on theconnection side and the swaged section located closer to the open endthan the swaged section located on the connection side. In the swaging,among the swaged sections, a swaged section other than the swagedsection located on the connection side begins to be primarily swaged.This allows strong force to be prevented from acting on the elastic bodyin a free state at a time and also allows the swaged section located onthe connection side to begin to be swaged in such a state that theelastic body is aligned on the open end side as compared to the casewhere the swaged sections begin to be simultaneously swaged. Therefore,since the misalignment of the elastic body can be reduced during swagingas compared to the case where the swaged sections begin to besimultaneously swaged, the misalignment of the connections between theconnector and the leads is reduced and therefore connection failure canbe prevented. In addition, since the pressure in the elastic body can beincreased by reducing the projection length of the swaged elastic bodyprotruding from the open end, sealing properties can be enhanced. Thus,better sealing properties and electrical connectivity can be ensured.

Herein, the expression “among the swaged sections, a swaged sectionother than the swaged section located on the connection side begins tobe primarily swaged” means that among the swaged sections, the swagedsection located on the open end side may begin to be swaged prior to theswaged section located on the connection side or a swaged sectionlocated closest to the open end may begin to be primarily swaged.Alternatively, the swaged section located on the connection side maybegin to be swaged in the course of swaging a swaged section other thanthe swaged section located on the connection side or the swaged sectionlocated on the connection side may begin to be swaged after the swagingof a swaged section other than the swaged section located on theconnection side is finished.

In the method for manufacturing the gas sensor according to the presentinvention, in the swaging, two of the swaged sections that are a firstswaged section located on the connection side and a second swagedsection located on the open end side are swaged and among the two swagedsections, the second swaged section may begin to be swaged prior to thefirst swaged section. This allows better sealing properties andelectrical connectivity to be ensured as compared to the case where thefirst swaged section and the second swaged section begin to besimultaneously swaged.

In the method for manufacturing the gas sensor according to the presentinvention, in the swaging, the elastic body may be swaged such that theinside diameter of a portion of the elastic body that corresponds to thefirst swaged section is greater than the inside diameter of a portion ofthe elastic body that corresponds to the second swaged section. Thisallows further better sealing properties and electrical connectivity tobe ensured because the first swaged section is prevented from affectingelectrical connectivity by inhibiting excessive force from acting on theconnections and sealing properties can be enhanced by sufficientlyswaging the second swaged section.

In the method for manufacturing the gas sensor according to the presentinvention, in the swaging, the elastic body may be swaged with apredetermined distance present between the first swaged section and thesecond swaged section in an axial direction of the elastic body. Thisallows the misalignment of the elastic body during swaging to be furtherreduced because the elongation of the elastic body can be absorbed by aportion corresponding to the predetermined distance in the case wherethe first swaged section begins to be swaged and the second swagedsection then begins to be swaged.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure.

FIG. 1 is a sectional view of a gas sensor 10 according to an embodimentof the present invention.

FIG. 2 is a sectional view of swaged sections of the gas sensor 10.

FIG. 3 is an illustration showing how an outer tube 46 and a rubber plug60 are swaged in the course of manufacturing the gas sensor 10.

FIGS. 4A and 4B are illustrations showing how the outer tube 46 and therubber plug 60 are swaged in the course of manufacturing the gas sensor10.

FIGS. 5A to 5C are illustrations showing how two swaged sections beginto be simultaneously swaged.

FIGS. 6A to 6C are illustrations showing how one of two swaged sectionsthat is located on the open end side begin to be primarily swaged.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described withreference to the attached drawings.

FIG. 1 is a sectional view of a gas sensor 10 according to an embodimentof the present invention. As shown in FIG. 1, the gas sensor 10 includesa sensor element 20. for measuring the concentration of a predeterminedgas component in measured gas, a protective cover 30 protecting an endportion of the sensor element 20, and a sensor assembly 40 including arubber plug 60 and a connector 50 electrically connected to the sensorelement 20. The gas sensor 10 is attached to, for example, a vehicle'sexhaust pipe and used to measure the concentration of a substance, suchas NO_(x) or O₂, contained in an exhaust gas which is measured gas.

The sensor element 20 is an element with a narrow elongated plate-likeshape and is composed of, for example, six stacked ceramic substrateseach including an oxygen-ion conducting solid electrolyte layer made ofzirconia (ZrO₂) or the like. Herein, an end portion of the sensorelement 20 that is located on the protective cover 30 side is referredto as a free end and an end portion of the sensor element 20 that islocated on the connector 50 is referred to as a base end. The front andback surfaces of the base end of the sensor element 20 each haveelectrodes (not shown) for applying a voltage to the sensor element 20or extracting the electromotive force or current generated depending onthe concentration of a gas component detected by the sensor element 20.The electrodes are arranged on the front and back surfaces of the sensorelement 20 and are electrically connected to an electrode (not shown)placed in the free end of the sensor element 20 through a conductingpath extending in the sensor element 20.

The protective cover 30 is placed so as to surround the periphery of thefree end of the sensor element 20. The protective cover 30 includes aninner protective sub-cover 31 covering the free end of the sensorelement 20 and an outer protective sub-cover 32 covering the innerprotective sub-cover 31. The inner protective sub-cover 31 istube-shaped and has an inner protective cover hole 31 a for introducingmeasured gas to the free end of the sensor element 20. The outerprotective sub-cover 32 has a bottomed cylindrical shape and also has,placed in the side surface, outer protective cover holes 32 a forintroducing measured gas. The inner protective sub-cover 31 and theouter protective sub-cover 32 are made of, for example, metal such asstainless steel.

The sensor assembly 40 includes a main fitting 41 made of metal, acylindrical inner tube 42 welded to the main fitting 41, a cylindricalouter tube 46 welded to the main fitting 41, the connector 50, therubber plug 60. The connector 50 is connected to the base end of thesensor element 20. The rubber plug 60 is attached to the outer tube 46.The main fitting 41 is attachable to, for example, automotive exhaustpipes using a male screw portion 41 a. The following members areenclosed in the main fitting 41 and the inner tube 42: a plurality ofceramic supporters 43 a to 43 c and ceramic powders 44 a and 44 b suchas talc powders. The ceramic powder 44 a is placed between the ceramicsupporters 43 a and 43 b and the ceramic powder 44 b is placed betweenthe ceramic supporters 43 b and 43 c. The ceramic supporters 43 a to 43c and the ceramic powders 44 a and 44 b are surrounded by a metal ring45, the inner wall of the main fitting 41, and the inner wall of theinner tube 42 and are thereby sealed. The outer tube 46 coverssurroundings of the inner tube 42, the sensor element 20, and theconnector 50 and has an open end 46 a (the upper end of the outer tube46 shown in FIG. 1). The rubber plug 60 is attached to the open end 46a.

The connector 50 includes a housing 51 made of a ceramic such assintered alumina and contact fittings 52 which are supported by thehousing 51 and which are in contact with the electrodes of the sensorelement 20. The contact fittings 52 extend outside the connector 50 andare electrically connected to leads 48 through connections 52 a whichare crimp contacts. In the connector 50, the number (for example, four,eight, or the like) of the contact fittings 52 corresponds to the numberof the electrodes placed on the front and back surfaces of the sensorelement 20. Therefore, the number of the connections 52 a is more thanone (for example, four, eight, or the like) and the number of the leads48 is also more than one (for example, four, eight, or the like).

The rubber plug 60 is located at the open end 46 a of the outer tube 46;is a member, made of fluoro-rubber, for sealing gaps between the outertube 46 and the leads 48 (the connections 52 a); and has through-holes60 a extending therein. The connections 52 a are placed in thethrough-holes 60 a and the leads 48 are inserted in the through-holes 60a. The plurality of through-holes are provided to accommodate theplurality of connections 52 a and leads 48. Since the gas sensor 10 isattached to a vehicle's exhaust pipe, the gas sensor 10 needs to becompact due to a limitation in installation space. Therefore, theconnections 52 a are placed in the through-holes 60 a, whereby thelength (length in axial direction) of the rubber plug 60 is limited andthe gas sensor 10 is made compact (the length of the outer tube 46 islimited). The rubber plug 60 contains a filler (aggregate) made of aninorganic material. The filler is an alumina (Al₂O₃) or silica (SiO₂)powder with a particle size of 0.1 μm to 10 μm and the content of thefiller is 1% to 30% by weight. The use of the filler allows the rubberplug 60 to have increased hardness.

The rubber plug 60 is radially swaged together with the outer tube 46and is thereby fixed in the outer tube 46. FIG. 2 shows swaged sectionsthereof in cross section. As shown in FIG. 2, two swaged sections arearranged in an axial direction of the outer tube 46 (the rubber plug60): one located on the connector 50 side (the sensor element 20 side)is referred to as a swaged section A ((A) in FIG. 2) and the otherlocated closer to the open end 46 a than the swaged section A (on theside on which the leads 48 extend outward) is referred to as a swagedsection B ((B) in FIG. 2). The swaged section A is one formed by swagingthe entire periphery of the outer tube 46 at sites (sites whichcorrespond to the connections 52 a in a radial direction of the outertube 46 and which are located directly above and under the connections52 a as shown in FIG. 2) corresponding to the connections 52 a betweenthe contact fittings 52 and the leads 48. The swaging width LA (thelength in the axial direction of the outer tube 46) of the swagedsection A is within the width (within the length in the axial directionof the outer tube 46 at the connections 52 a) of the connections 52 a.The swaged section B is apart from the swaged section A at apredetermined distance LS and has a swaging width LB equal to theswaging width LA. When the inside diameter of a portion of the outertube 46 that corresponds to the swaged section A and the inside diameterof a portion of the outer tube 46 that corresponds to the swaged sectionB are expressed as inside diameter φA and inside diameter φB,respectively, the relation “inside diameter φA>inside diameter φB”holds. That is, the swaged section B is one more heavily swaged than theswaged section A. In this embodiment, in the swaged sections A and B,the inside diameter and thickness of the unswaged outer tube 46 areinvariant and therefore inside diameter φA and inside diameter φBcorrespond to the outside diameter of the swaged rubber plug 60.

The rubber plug 60 is used to the seal the open end 46 a of the outertube 46. Therefore, if the rubber plug 60 is not sufficiently swaged,then sealing properties are not ensured and moisture and gases otherthan measured gas leak into the outer tube 46 to adversely affect thedetection accuracy of the sensor element 20 in some cases. On the otherhand, the leads 48 are inserted in the rubber plug 60 and theconnections 52 a between the contact fittings 52 and the leads 48 areplaced in the rubber plug 60. Therefore, if the whole of the rubber plug60 is excessively swaged, then excessive force acts on the leads 48 andthe connections 52 a. When excessive force acts on the leads 48 and theconnections 52 a, the leads 48 are likely to be broken, the resistanceof the leads 48 becomes unstable, the connections 52 a become faulty,and/or the contact of the connections 52 a cause shorts; hence,electrical connectivity may possibly be impaired. Alternatively, if asite corresponding to the swaged section A is not swaged, then theconnections 52 a are not secured in the through-holes 60 a and thereforethe misalignment of the connections 52 a (the contact fittings 52) islikely to be caused by vibrations from vehicles. Hence, in this case,electrical connectivity may possibly be impaired. Therefore, in thisembodiment, the swaged section B is more heavily swaged than the swagedsection A, whereby sealing properties are ensured and leaking isprevented. Since the swaged section A is more lightly swaged than theswaged section B, excessive force is prevented from acting on theconnections 52 a with the connections 52 a secured and good electricalconnectivity is achieved. The reason why the inside diameter φA of theswaged section A and the inside diameter φB of the swaged section B areset such that the relation “inside diameter φA>inside diameter φB” holdsis that the prevention of leaking and the prevention of electricalconnection failure are both achieved.

In the swaged section B, in order to ensure sealing properties, theswaging ratio is within the range of 8% to 14%, the swaging ratio beingdetermined by dividing the difference (inside diameter beforeswaging−inside diameter φB after swaging) in inside diameter between theunswaged outer tube 46 and the swaged outer tube 46 by the insidediameter of the unswaged outer tube 46. The inside diameter of theportion of the unswaged outer tube 46 that corresponds to the swagedsection B, is used as the inside diameter before swaging. Instead, theinside diameter of a portion (an unswaged portion located between theswaged sections A and B) of the swaged outer tube 46, the portioncorresponding to the predetermined distance LS, may be used.Furthermore, in the swaged section A, the inside diameter φA is set tobe slightly greater than the inside diameter φB such that swaging isslight and sealing properties are not significantly impaired. Inparticular, the inside diameter variance determined by dividing thedifference between the inside diameter φA and the inside diameter φB bythe inside diameter φB is 1% to 5%. That is, the inside diameter φA is1% to 5% greater than the inside diameter φB. Furthermore, in thisembodiment, since the hardness of the rubber plug 60 is increased byadding the filler to as described above, the durability of the rubberplug 60 can be increased. Therefore, the breakage of the rubber plug 60can be reduced and obtained sealing properties can be maintained for along period. In particular, the effect of adding the filler issignificant because the gas sensor 10 is one used in vehicles and therubber plug 60 is exposed to gas at a high temperature of higher than250° C. and therefore is in a degradable environment.

A method for manufacturing the gas sensor 10 is described below. First,the main fitting 41 and the inner tube 42 are assembled by welding so asto be coaxial with each other. After the ceramic supporter 43 a, theceramic powder 44 a, the ceramic supporter 43 b, the ceramic powder 44b, and the ceramic supporter 43 c are provided in the inner tube 42 inthat order from the main fitting 41, the metal ring 45 is inserted inthe inner tube 42. Next, the sensor element 20 is passed through theceramic supporter 43 c, the ceramic powder 44 b, the ceramic supporter43 b, the ceramic powder 44 a, and the ceramic supporter 43 a in thatorder from the metal ring 45. The ceramic supporters 43 a to 43 c, theceramic powders 44 a and 44 b, and the metal ring 45 each have a holethrough which the sensor element 20 can be passed. The metal ring 45 andthe main fitting 41 are pressed in a direction in which the metal ring45 and the main fitting 41 approach each other, whereby the ceramicpowders 44 a and 44 b are compressed. In such a state, a portion (anupper portion in FIG. 1) of the inner tube 42 that is located outsidethe metal ring 45 is reduced in diameter by swaging and a portion of theinner tube 42 that contains the ceramic powder 44 b is also reduced indiameter by swaging, a primary assembly including the main fitting 41and the sensor element 20 is obtained.

After the primary assembly is obtained as described above, the innerprotective sub-cover 31 and the outer protective sub-cover 32 are weldedto the main fitting 41, whereby the protective cover 30 is formed. Theouter tube 46 is welded to the main fitting 41. Subsequently, the rubberplug 60 having the through-holes 60 a is prepared. Herein, a rubbermaterial for the rubber plug 60 is prepared in such a way that thefiller, which is the alumina (Al₂O₃) with a particle size of 0.1 μm to10 μm, is added to a rubber component such as fluoro-rubber such thatthe content thereof is 1% to 30% by weight, followed by kneading with amixer or the like. The filler is not limited to the alumina (Al₂O₃) andmay be a silica (SiO₂). The rubber material, prepared as describedabove, containing the filler is shaped so as to have a necessary formand size and is subjected to a step necessary to form the through-holes60 a, whereby the rubber plug 60 is obtained. The leads 48 are passedthrough the through-holes 60 a of the rubber plug 60 and the connections52 a of the contact fittings 52 are connected to the leads 48, wherebythe connector 50 is prepared. The connector 50 is connected to the baseend of the sensor element 20. The rubber plug 60 is inserted in the openend 46 a of the outer tube 46. Next, the outer tube 46 and the rubberplug 60 are reduced in diameter by swaging, whereby the rubber plug 60is fixed to the outer tube 46. FIGS. 3 and 4 show how the outer tube 46and the rubber plug 60 are swaged in the course of manufacturing the gassensor 10.

As shown in FIG. 3, swaging is performed using swaging tools 102 set toa swaging machine (not shown) and a pressing tool 104 pressing the backside of the swaging tools 102. The swaging tools 102 each include a bump102 a for swaging the swaged section A and a bump 102 b for swaging theswaged section B. As shown in an enlarged view in FIG. 3, the height haof the bump 102 a is slightly different from the height hb of the bump102 b. The height hb is greater than the height ha by Δh (for example,0.1 mm, 0.2 mm, or the like). The swaging tools 102 have such a formthat a cylindrical member is divided into eight pieces at 45°.Therefore, in the case where eight of the swaging tools 102 are set tothe swaging machine so as to direct the bumps 102 a and 102 b inward andthe gas sensor 10 is set to the center surrounded by the swaging tools102, the swaging tools 102 are arranged around the outer tube 46, whichis cylindrical. An outside back surface 102 c of each swaging tool 102and an inside pressing surface 104 a of the pressing tool 104 aretapered at substantially the same angle. Therefore, when the pressingtool 104 moves leftward to bring the pressing surface 104 a into contactwith the back surface 102 c as shown in FIG. 3, the swaging tool 102(the bumps 102 a and 102 b) are pressed by the pressing tool 104 andtherefore move substantially in parallel from outside toward the centerside (the outer tube 46 side).

When the pressing tool 104 further moves leftward from a state shown inFIG. 3 and the swaging tool 102 move to the center side to abut theouter tube 46, swaging starts (refer to FIG. 4A). Since the height ha ofthe bump 102 a and the height hb of the bump 102 b are slightlydifferent from each other, the bump 102 b abuts the outer tube 46 priorto the bump 102 a as shown in an enlarged view in FIG. 4A. That is, thebump 102 b starts swaging prior to the bump 102 a. Therefore, the swagedsection B begins to be swaged prior to the swaged section A. Thepressing tool 104 further moves leftward and therefore the swaging tool102 are moved (pressed) toward the center side (the outer tube 46 side),whereby swaging is performed. When the pressing tool 104 reaches apredetermined position, swaging ends (refer to FIG. 4B). Herein, sincethe height hb is greater than the height ha by Δh, the bump 102 b isgreater in indentation depth than the bump 102 a. Therefore, the bump102 b is greater in swaging depth than the bump 102 a; hence, the insidediameter φB of the swaged section B is less than the inside diameter φAof the swaged section A. The gas sensor 10 in FIG. 1 is obtained by sucha manufacturing method including swaging.

As described above, in the method for manufacturing the gas sensor 10,among the two swaged sections A and B, the swaged section B begins to beprimarily swaged in the course of swaging the outer tube 46 and rubberplug 60. For comparison, FIGS. 5A to 5C show how two swaged sectionsbegin to be simultaneously swaged. FIGS. 6A to 6C show how one of twoswaged sections that is located on the open end side begins to beprimarily swaged like this embodiment. In FIGS. 5A to 5C and 6A to 6C,the leads 48, the connections 52 a, the through-holes 60 a, or the likeare not shown. As shown in FIGS. 5A to 5C, since the two swaged sectionsA and B begin to be simultaneously swaged (FIG. 5A), relatively strongforce acts on the rubber plug 60 in a free state. Also, the elongationof rubber between (inside) the swaged sections A and B repels (insideelongation is restricted) and therefore rubber is likely to extendoutward. That is, in the swaged section A, the rubber plug 60 relativelysignificantly extends leftward, and in the swaged section B, the rubberplug 60 relatively significantly extends rightward (in a direction inwhich the rubber plug 60 protrudes from the outer tube 46). Therefore,the projection length t0 of the rubber plug 60 protruding from the outertube 46 is relatively large (FIG. 5B). The progression of swagingincreases the elongation of the rubber plug 60 and also increases theprojection length t of the rubber plug 60 protruding from the outer tube46 (FIG. 5C). The connector 50, which is not shown, is present on theleft side in FIGS. 5A to 5B and therefore the leftward elongation of therubber plug 60 is more likely to be restricted as compared to therightward elongation thereof. On the other hand, as shown in FIGS. 6A to6C, among the two swaged sections A and B, the swaged section B islocated on the open end side and begins to be primarily swaged (FIG.6A); hence, the force acting on the rubber plug 60 at the start ofswaging is less as compared to a comparative example and the leftward(inward) elongation of rubber in the swaged section B is unlikely to berestricted. Therefore, the projection length t0 of the rubber plug 60protruding from the outer tube 46 is less as compared to a comparativeexample (FIG. 6B). When the swaged section A begins to be swaged, rubberin the swaged section B acts so as to restrict the elongation of therubber plug 60 due to the swaging of the swaged section A because theswaged section B has already begun to be swaged. Since only the swagedsection B begins to be primarily swaged, the swaged section A begins tobe swaged in such a state that the rubber plug 60 is axially aligned atthe swaged section B. Therefore, though swaging proceeds, the elongationof the rubber plug 60 is absorbed by the portion, located between theswaged sections A and B, corresponding to the predetermined distance LS;hence, the projection length t of the rubber plug 60 protruding from theouter tube 46 can be reduced as compared to the comparative example(FIG. 6C). Thus, the misalignment of the rubber plug 60 due to swagingis reduced and therefore the rubber plug 60 after swaging can be kept atsubstantially the same position. Since the projection length t of therubber plug 60 protruding from the outer tube 46 is reduced withoutvarying the indentation depth during swaging as described above, thepressure in the rubber plug 60 in the outer tube 46 can be increased.Therefore, sealing properties of the rubber plug 60 can be maintainedfor a long period. Since the position of the rubber plug 60 is notsignificantly varied before and after swaging (misalignment is reducedand substantially the same position is kept), the axial force (tensileforce) applied to the leads 48 and the connections 52 a during swagingis reduced and therefore the breakage of the leads 48 and the failure ofthe connections 52 a can be prevented from occurring. These are thereasons why the swaged section B begins to be primarily swaged duringswaging.

The correspondence between elements of this embodiment and elements ofthe present invention is described below. The sensor element 20corresponds to a “sensor element” of the present invention, theconnector 50 corresponds to a “connector” of the present invention, theouter tube 46 corresponds to a “tubular body” of the present invention,the leads 48 correspond to “leads” of the present invention, the rubberplug 60 corresponds to an “elastic body” of the present invention, theswaged section A corresponds to a “first swaged section” of the presentinvention, and the swaged section B corresponds to a “second swagedsection” of the present invention.

According to this embodiment, the outer tube 46 and the rubber plug 60are swaged at two sites, that is, the swaged section A, which is locatedon the connections 52 a, and the swaged section B, which is located onthe open end 46 a side of the outer tube 46, such that the insidediameter φA of the portion of the rubber plug 60 that corresponds to theswaged section A is greater than the inside diameter φB of the portionof the rubber plug 60 that corresponds to the swaged section B.Therefore, the swaged section B is more heavily swaged than the swagedsection A, whereby sealing properties are ensured and leakage can beprevented. The swaged section A is more lightly swaged than the swagedsection B, whereby the failure of the connections 52 a and the like canbe prevented. In the swaged section B, the swaging ratio is set withinthe range of 8% to 14% and therefore sealing properties can be reliablyensured. Furthermore, in the swaged section A, the swaged section A isset to be 1% to 5% greater than the swaged section B; hence, the swagedsection A is more lightly swaged than the swaged section B and sealingproperties can be prevented from being significantly impaired. Since therubber plug 60 contains the filler, sealing properties can be maintainedfor a long period by increasing the pressure in the rubber plug 60.These allow better sealing properties and electrical connectivity to beensured.

According to this embodiment, in swaging, among the two swaged sectionsA and B, the swaged section B begins to be primarily swaged; hence,strong force can be prevented from acting on the rubber plug 60 in afree state at a time and the swaged section A can begin to be swaged insuch a state that the portion of the rubber plug 60 that corresponds tothe swaged section B is aligned as compared to the case where the swagedsections A and B begin to be simultaneously swaged. Therefore, theposition of the rubber plug 60 can be prevented from being significantlyvaried and the rubber plug 60 can be prevented from protruding from theouter tube 46; hence, the breakage of the leads 48 and the failure ofthe connections 52 a can be prevented from occurring and sealingproperties can be maintained for a long period by increasing thepressure in the rubber plug 60. In addition, the elongation of therubber plug 60 can be absorbed by the portion, located between theswaged sections A and B, corresponding to the predetermined distance LSand therefore the pressure in the rubber plug 60 can be furtherincreased.

The present invention is not limited to this embodiment and variousmodifications can be made within the technical scope of the presentinvention.

In this embodiment, the swaged section A is a site corresponding to theconnections 52 a and the swaging width LA of the swaged section A iswithin the width of the connections 52 a. Instead, the width of theconnections 52 a may be within the swaging width LA of the swagedsection A or the swaging width LA of the swaged section A may partlyoverlap the width of the connections 52 a.

In this embodiment, the two swaged sections A and B are swaged. Instead,three or more sites may be swaged. In the case of swaging three or moresites, it is only necessary that the inside diameter φA of the swagedsection A, which is the site corresponding to the connections 52 a, isgreater than the inside diameter φA of a swaged section other than theswaged section A. In a step of swaging three or more sites, it is onlynecessary that a swaged section other than the swaged section A beginsto be primarily swaged.

In this embodiment, the inside diameter φA of the portion of the rubberplug 60 that corresponds to the swaged section A is greater than theinside diameter φB of the portion of the rubber plug 60 that correspondsto the swaged section B. Instead, the inside diameter φA and the insidediameter φB may be the same. However, as described above, in order toensure better sealing properties and electrical connectivity, the insidediameter φA is preferably greater than the inside diameter φB.

In this embodiment, the swaged section A begins to be swaged in thecourse of swaging the swaged section B. Instead, after the swagedsection B is swaged, the swaged section A may begin to be swaged.

In this embodiment, the rubber plug 60 is the member made offluoro-rubber. Instead, the rubber plug 60 may be made of anothermaterial, such as a heat-resistant resin, capable of sealing the openend 46 a of the outer tube 46.

In this embodiment, the rubber plug 60 contains the filler. Instead, therubber plug 60 need not contain the filler.

In this embodiment, the swaged sections A and B are swaged with theswaging tools 102 common thereto. Instead, the swaged sections A and Bmay be separately swaged with separate swaging tools.

In this embodiment, the height ha of the bumps 102 a of the swagingtools 102 is different from the height hb of the bumps 102 b thereof.Instead, the height ha of the bumps 102 a may be the same as the heighthb of the bumps 102 b and the swaging tools 102 may be different inindentation depth from each other.

In this embodiment, the predetermined distance LS is present between theswaged sections A and B. Instead, the swaged sections A and B may bestepwise connected with no distance therebetween.

In this embodiment, the swaging width LA of the swaged section A is thesame as the swaging width LB of the swaged section B. Instead, theswaging width LA of the swaged section A may be different from theswaging width LB of the swaged section B. For example, the swaging widthLB of the swaged section B may be greater than the swaging width LA ofthe swaged section A. This allows sealing properties to be furtherensured and leakage to be further prevented because the swaging width LBof the swaged section B is large and also allows excessive force to beprevented from acting on the connections 52 a because the swaging widthLA of the swaged section A is small.

EXAMPLES Preliminary Test

Before the gas sensor 10 shown in FIG. 10 was manufactured, thefollowing test was carried out: a preliminary test to determine therange of the swaging ratio of the inside diameter φB as the referenceinside diameter of the swaged outer tube 46. In the preliminary test,the following sensors were prepared: gas sensors subjected tosingle-stage swaging at a single swaged section and gas sensorssubjected to two-stage swaging at two swaged sections. In thepreliminary test, unlike the above embodiment, the gas sensors wereswaged so as to have the same inside diameter. Seven of the gas sensorssubjected to single-stage swaging and seven of the gas sensors subjectedto two-stage swaging were prepared and were swaged such that the insidediameter before swaging was reduced from 11.8 mm to 11.0 mm (about 7%),10.8 mm (about 8%), 10.6 mm (about 10%), 10.4 mm (about 12%), 10.2 mm(about 14%), 10.0 mm (about 15%), or 9.8 mm (about 17%) by swaging (eachparenthesized value is the swaging ratio). The outside diameter of theunswaged rubber plug 60 was 11.0 mm. In the preliminary test, eachprepared gas sensor was attached to a gas pipe similar to an automotiveexhaust pipe. As shown in heating conditions in Table 1, a heating testwas continuously carried out for 100 hours in such a way that the rubberplug 60 is exposed to high temperature, about 250° C., by introducingabout 850° C. gas into the gas pipe using a gas burner. After theheating test was finished, a leakage test to check the leakage of airwas carried out in such a way that air with a static pressure of 0.1 MPawas applied to the gas sensor from the lead 48 side. Subsequently, therubber plug 60 was taken out of the gas sensor and was checked for thepresence of cracks, whereby the rubber plug 60 was evaluated fordurability.

TABLE 1 HEATING DEVICE C₃H₈ BURNER GAS TEMPERATURE 850° C. RUBBER PLUG250° C. TEMPERATURE HEATING TIME 100 hours

Table 2 shows results of the preliminary test. In the leakage test, thegas sensors, subjected to single-stage swaging, having an insidediameter φB of 10.6 mm to 11.0 mm had leaks and those having an insidediameter φB of 9.8 mm to 10.4 mm had no leaks. In Table 2, the symbol“B” denotes the absence of leaks and the symbol “D” denotes the presenceof leaks problematic in practical use. The gas sensor, subjected totwo-stage swaging, having an inside diameter φB of 11.0 mm had leaks andthe others having an inside diameter φB of 9.8 mm to 10.8 mm had noleaks. In the evaluation of durability, the gas sensors, subjected tosingle- or two-stage swaging, having an inside diameter φB of 10.2 mm to11.0 mm had no cracks (denoted by “B”) and were good in durability.However, those having an inside diameter φB of 9.8 mm or 10.0 mm hadcracks (denoted by “D”) and were poor in durability.

TABLE 2 LEAKAGE TEST DURABILITY OF RUBBER PLUG TWO-STAGE SWAGINGTWO-STAGE SWAGING REFERENCE INSIDE (TWO-STAGE WITH (TWO-STAGE WITHDIAMETER SWAGING SINGLE-STAGE SAME INSIDE SINGLE-STAGE SAME INSIDEφB(mm) RATIO SWAGING DIAMETER) SWAGING DIAMETER) φ11.0  7% D D B B φ10.8 8% D B B B φ10.6 10% D B B B φ10.4 12% B B B B φ10.2 14% B B B B φ10.015% B B D D φ9.8 17% B B D D

The results of the preliminary test indicate the following. First, thereference inside diameter (inside diameter φB) capable of preventingleakage and keeping durability is preferably within the range of 10.2 mmto 10.8 mm, that is, the swaging ratio is preferably within the range of8% to 14%. In the above embodiment, the inside diameter TA is greaterthan the inside diameter φB; hence, one having a high leakage preventioneffect only by a single stage of the inside diameter φB is required.Therefore, the inside diameter φB is more preferably within the range of10.2 mm to 10.4 mm, that is, the swaging ratio is more preferably withinthe range of 12% to 14%.

Evaluation Test 1

For the inside diameter φB determined as the reference inside diameterin the preliminary test, gas sensors for comparative examples in whichthe inside diameter φA was determined at an inside diameter variance of0% (the same diameter) and gas sensors for examples in which the insidediameter φA was determined at an inside diameter variance within apredetermined range were prepared, followed by Evaluation Test 1. In thepreliminary test, the preferred range of the inside diameter φB was 10.2mm to 10.8 mm; hence, three sizes, 10.8 mm, 10.4 mm, and 10.2 mm, wereused as values of the inside diameter φB. The inside diameter varianceof the examples was within the range of 0.1% to 7% and was set to 0.1%,0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 7%. In Evaluation Test 1, a heatingtest was carried out in substantially the same manner as that describedin the preliminary test. After the heating test was finished, the aboveleakage test was carried out. Subsequently, the elongation ΔL of thewhole rubber plug 60 was investigated. As the elongation ΔL of the wholerubber plug 60 as well as the projection length t of the rubber plug 60increases, the tensile force acting on the leads 48 increases; hence,connection failure or disconnection is likely to occur and thereforeelectrical connectivity is reduced in some cases. The increase inelongation ΔL of the rubber plug 60 leads to the reduction of sealingproperties because the pressure in the rubber plug 60 is reduced.Herein, it has been grasped that in the rubber plug 60 having an outsidediameter of 11.0 mm and a length L of 14.5 mm in an initial state beforeswaging, electrical connectivity or sealing properties are affected insome cases when the elongation ΔL is 2.5 mm or more and such influenceis significant when the elongation ΔL is 3.0 mm or more. Therefore, anelongation ΔL of less than 2.5 mm was rated as “B”, an elongation ΔL of2.5 mm to less than 3.0 mm was rated as “C”, and an elongation ΔL of 3.0mm or more was rated as “D”. In the manufacture of the gas sensor 10,the projection length t of the rubber plug 60 protruding from the outertube 46 is preferably about 1 mm and is aimed at the range of 1 mmplus/minus 0.5 mm (the range of a lower limit of 0.5 mm to an upperlimit of 1.5 mm).

Table 3 shows results of Experimental Examples 1 to 10 in the case of aninside diameter φB of 10.8 mm. Experimental Example 1 corresponds to acomparative example and Experimental Example 2 to 10 correspond toexamples. In the leakage test, Experimental Example 1 to 8 (an insidediameter variance of 0% or 0.1% to 5%) had no leaks and were rated as“B” and Experimental Examples 9 and 10 (an inside diameter variance of6% or 7%) had slight leaks and were rated as “C”. In results of theleakage test, the symbol “B” denotes the absence of leaks as describedabove and the symbol “C” denotes the presence of slight leaks notproblematic in practical use. For the elongation ΔL of the whole rubberplug 60, Experimental Example 1 (an inside diameter variance of 0%)exhibited 2.5 mm and was rated as “C” and Experimental Examples 2 to 10(an inside diameter variance of 0.1% to 7%) exhibited less than 2.5 mmand were rated as “B”. Therefore, for comprehensive evaluation in thecase of an inside diameter φB of 10.8 mm, Experimental Examples 2 to 8(an inside diameter variance of 0.1% to 5%) were rated as “A” andExperimental Examples 1, 9, and 10 were rated as “B”. For comprehensiveevaluation, the symbol “A” denotes that both the leakage test and theelongation ΔL are rated as “B”, the symbol “B” denotes that one of theleakage test and the elongation ΔL is rated as “B” and the other israted as “C”, and the symbol “D” denotes that one of the leakage testand the elongation ΔL is rated as “D”.

TABLE 3 INSIDE DIAMETER LEAKAGE ELONGATION COMPREHENSIVE VARIANCEREFERENCE INSIDE DIAMETER φB: 10.8 mm TEST ΔL EVALUATION 0% EXPERIMENTALEXAMPLE 1 φA: 10.8 mm B 2.5 mm(Δ) B 0.1%  EXPERIMENTAL EXAMPLE 2 φA:10.81 mm B 2.0 mm(∘) A 0.5%  EXPERIMENTAL EXAMPLE 3 φA: 10.85 mm B 1.9mm(∘) A 1% EXPERIMENTAL EXAMPLE 4 φA: 10.91 mm B 1.8 mm(∘) A 2%EXPERIMENTAL EXAMPLE 5 φA: 11.02 mm B 1.6 mm(∘) A 3% EXPERIMENTALEXAMPLE 6 φA: 11.12 mm B 1.4 mm(∘) A 4% EXPERIMENTAL EXAMPLE 7 φA: 11.23mm B 1.3 mm(∘) A 5% EXPERIMENTAL EXAMPLE 8 φA: 11.34 mm B 1.1 mm(∘) A 6%EXPERIMENTAL EXAMPLE 9 φA: 11.45 mm C 1.0 mm(∘) B 7% EXPERIMENTALEXAMPLE 10 φA: 11.56 mm C 0.8 mm(∘) B

Table 4 shows results of Experimental Examples 11 to 20 in the case ofan inside diameter φB of 10.4 mm. Experimental Example 11 corresponds toa comparative example and Experimental Examples 12 to 20 correspond toexamples. In the leakage test, Experimental Examples 11 to 19 (an insidediameter variance of 0% or 0.1% to 6%) had no leaks and were rated as“B” and Experimental Example 20 (an inside diameter variance of 7%) hadslight leaks and were rated as “C”. For the elongation ΔL of the wholerubber plug 60, Experimental Example 11 (an inside diameter variance of0%) exhibited 3.5 mm and was rated as “D”, Experimental Example 12 (aninside diameter variance of 0.1%) exhibited 2.5 mm and was rated as “C”,and Experimental Examples 13 to 20 (an inside diameter variance of 0.5%to 7%) exhibited less than 2.5 mm and were rated as “B”. Therefore, forcomprehensive evaluation in the case of an inside diameter φB of 10.4mm, Experimental Examples 13 to 19 (an inside diameter variance of 0.5%to 6%) were rated as “A”, Experimental Examples 12 and 20 (an insidediameter variance of 0.1% or 7%) were rated as “B”, and ExperimentalExample 11 (an inside diameter variance of 0%) was rated as “D”.

TABLE 4 INSIDE DIAMETER LEAKAGE ELONGATION COMPREHENSIVE VARIANCEREFERENCE INSIDE DIAMETER φB:10.4 mm TEST ΔL EVALUATION 0% EXPERIMENTALEXAMPLE 11 φA: 10.4 mm B 3.5 mm(x) D 0.1%  EXPERIMENTAL EXAMPLE 12 φA:10.41 mm B 2.5 mm(Δ) B 0.5%  EXPERIMENTAL EXAMPLE 13 φA: 10.45 mm B 2.2mm(∘) A 1% EXPERIMENTAL EXAMPLE 14 φA: 10.50 mm B 2.0 mm(∘) A 2%EXPERIMENTAL EXAMPLE 15 φA: 10.61 mm B 1.8 mm(∘) A 3% EXPERIMENTALEXAMPLE 16 φA: 10.71 mm B 1.6 mm(∘) A 4% EXPERIMENTAL EXAMPLE 17 φA:10.82 mm B 1.4 mm(∘) A 5% EXPERIMENTAL EXAMPLE 18 φA: 10.92 mm B 1.2mm(∘) A 6% EXPERIMENTAL EXAMPLE 19 φA: 11.02 mm B 1.1 mm(∘) A 7%EXPERIMENTAL EXAMPLE 20 φA: 11.13 mm C 1.0 mm(∘) B

Table 5 shows results of Experimental Examples 21 to 30 in the case ofan inside diameter φB of 10.2 mm. Experimental Example 21 corresponds toa comparative example and Experimental Examples 22 to 30 correspond toexamples. In the leakage test, all of Experimental Examples 21 to 30 (aninside diameter variance of 0% or 0.1% to 7%) had no leaks and wererated as “B”. For the elongation ΔL of the whole rubber plug 60,Experimental Example 21 (an inside diameter variance of 0%) exhibited4.0 mm and was rated as “D”, Experimental Examples 22 and 23 (an insidediameter variance of 0.1% or 0.5%) exhibited 2.5 mm to less than 3.0 mmand were rated as “C”, and Experimental Examples 24 to 30 (an insidediameter variance of 1% to 7%) exhibited less than 2.5 mm and were ratedas “B”. Therefore, for comprehensive evaluation in the case of an insidediameter φB of 10.2 mm, Experimental Examples 24 to 30 (an insidediameter variance of 1% to 7%) were rated as “A”, Experimental Examples22 and 23 (an inside diameter variance of 0.1% or 0.5%) were rated as“B”, and Experimental Example 21 was rated as “D”.

TABLE 5 INSIDE DIAMETER LEAKAGE ELONGATION COMPREHENSIVE VARIANCEREFERENCE INSIDE DIAMETER φB: 10.2 mm TEST ΔL EVALUATION 0% EXPERIMENTALEXAMPLE 21 φA: 10.2 mm B 4.0 mm(x) D 0.1%  EXPERIMENTAL EXAMPLE 22 φA:10.21 mm B 2.8 mm(∘) B 0.5%  EXPERIMENTAL EXAMPLE 23 φA: 10.25 mm B 2.6mm(∘) B 1% EXPERIMENTAL EXAMPLE 24 φA: 10.30 mm B 2.4 mm(∘) A 2%EXPERIMENTAL EXAMPLE 25 φA: 10.40 mm B 2.0 mm(∘) A 3% EXPERIMENTALEXAMPLE 26 φA: 10.51 mm B 1.9 mm(∘) A 4% EXPERIMENTAL EXAMPLE 27 φA:10.61 mm B 1.8 mm(∘) A 5% EXPERIMENTAL EXAMPLE 28 φA: 10.71 mm B 1.5mm(∘) A 6% EXPERIMENTAL EXAMPLE 29 φA: 11.81 mm B 1.3 mm(∘) A 7%EXPERIMENTAL EXAMPLE 30 φA: 11.91 mm B 1.1 mm(∘) A

The results of Evaluation Test 1 indicate the following. Comparativeexamples (Experimental Examples 1, 11, and 21) with an inside diametervariance of 0% were rated as “B” in the case of an inside diameter φB of10.8 mm or were rated as “D” in the case of an inside diameter φB of10.4 mm or 10.2 mm because the elongation ΔL of the whole rubber plug 60was large. Therefore, it is conceivable that an inside diameter varianceof 0% adversely affects electrical connectivity with relatively highprobability. On the other hand, examples (Experimental Examples 2 to 10,12 to 20, and 22 to 30) with an inside diameter variance of 0.1% to 7%were all rated as “A” or “B”. Therefore, in these examples, leaks andthe reduction of electrical connectivity can be well prevented. Inparticular, examples (Experimental Examples 4 to 8, 14 to 18, and 24 to28) with an inside diameter variance of 1% to 5% were all rated as “A”.That is, in the examples with an inside diameter variance of 1% to 5%,leaks and the reduction of electrical connectivity can be further wellprevented regardless of the value of the inside diameter φB.

The above results of the preliminary test and Evaluation Test 1 indicatethat for the inside diameter φB, the swaging ratio is preferably withinthe range of 8% to 14% (the range of 10.2 mm to 10.8 mm) and morepreferably within the range of 12% to 14% (the range of 10.2 mm to 10.4mm). The inside diameter variance determined by dividing the differencebetween the inside diameter φA and the inside diameter φB by the insidediameter φB is preferably within the range of 1% to 5%. Therefore, as anexample of the size of a swaged section in an example, it is conceivablethat the inside diameter φB is adjusted to 10.4 mm within the range of10.2 mm and 10.4 mm and the inside diameter variance is adjusted to 2%in the range of 1% to 5%. That is, the inside diameter φB was adjustedto 10.4 mm, the inside diameter variance was adjusted to 2% with respectto an inside diameter φB of 10.4 mm, and the inside diameter φA wasadjusted to 10.6 mm. Furthermore, the swaging width LA and the swagingwidth LB were both adjusted to 2.5 mm and the swaging distance LS wasadjusted to 3.5 mm.

Evaluation Test 2

Thirty gas sensors 10 including swaged sections having a size determinedas described above were manufactured by a method in which a the swagedsection B begins to be swaged prior to the swaged section A as describedin the above embodiment, followed by measuring the projection length tof each rubber plug 60. Table 6 shows the measurement results. Theprojection length t ranged from 0.84 mm at minimum to 1.19 mm at maximumand was 1.04 mm on average. The projection length t was within the rangeof 1.0±0.5 mm, which is a target value as described above. This resultwas better than a result obtained by allowing the swaged sections A andB to begin to be simultaneously swaged. Therefore, in the gas sensors 10manufactured by the method described in the above embodiment, the effectof preventing leaks and the effect of preventing the reduction ofelectrical connectivity are high.

TABLE 6 PROJECTION No. LENGTH t(mm) 1 1.19 2 0.84 3 1.08 4 0.91 5 0.89 60.99 7 1.12 8 1.00 9 1.05 10 1.10 11 1.05 12 1.13 13 1.06 14 0.98 151.02 16 1.14 17 0.89 18 0.92 19 1.03 20 1.11 21 1.06 22 1.16 23 1.16 241.10 25 1.05 26 1.00 27 1.12 28 0.98 29 1.10 30 1.02 MAX 1.19 MIN 0.84AVE 1.04

What is claims is:
 1. A method for manufacturing a gas sensor includinga sensor element capable of detecting the concentration of measured gas;a connector electrically connected to the sensor element; a tubular bodyin which the sensor element and the connector are placed and which hasan open end; leads which are connected to the connector and which extendoutward from the open end of the tubular body; and an elastic body whichis placed in the tubular body so as to seal the open end, in whichconnections between the connector and the leads are placed, and throughwhich the leads extend, the method comprising: radially swaging thetubular body and the elastic body at a plurality of swaged sectionsincluding a swaged section located on the connection side and a swagedsection located closer to the open end than the swaged section locatedon the connection side, the swaging including, among the plurality ofswaged sections, a swaged section other than the swaged section locatedon the connection side to begin to be primarily swaged.
 2. The methodfor manufacturing the gas sensor according to claim 1, wherein theswaging includes the swaged sections, including a first swaged sectionlocated on the connection side and a second swaged section located onthe open end side, being swaged, and among the swaged sections, thesecond swaged section begins to be swaged prior to the first swagedsection.
 3. The method for manufacturing the gas sensor according toclaim 2, wherein the swaging includes the tubular body and the elasticbody being swaged such that the inside diameter of a portion of theelastic body corresponding to the first swaged section is greater thanthe inside diameter of a portion of the elastic body corresponding tothe second swaged section.
 4. The method for manufacturing the gassensor according to claim 2, wherein the swaging includes the tubularbody and the elastic body being swaged with a predetermined distancepresent between the first swaged section and the second swaged sectionin an axial direction of the elastic body.